Pumps of such type have been known in the art for a considerable time and are used at present in medicine for transferring biological fluids by pump.
Operation of these pumps is based on the principle that while an operating head is rotated, its roller member (or members) travels along the resilient tube in the direction of fluid transference, compressing the tube at the point of its contact with the rollers. Displacement of a contracted section of the tube's aperture results in pushing through the fluid along the tube in a manner which is similar to pushing through, for example, food during peristalsis (periodic wave-like contraction) of intestines. Accordingly, in view of their operating principle, the pumps of this type are also called "peristaltic".
The major task to be solved by such pumps consists in ensuring effective transference of blood at a required flow rate (volume to time), minimally affecting the transferred biological fluid. This latter condition is especially important because blood contains form elements such as erythrocytes, which are easily destructible by mechanical actions (impacts, shaking, vibration, etc.). Destruction of blood form elements (also known as "hemolysis") unavoidably arising during transference of blood to a patient, leads particularly to such an undesirable phenomenon as after-transfusion fever, which is a result of the human body's reaction to dissolved substances in blood which have separated from erythrocytes and other form elements destroyed during blood transference.
This reaction of the patient's body is stronger when the amount of blood subject to transference to the patient is greater. Thus, the more dramatic is the condition of a person and the greater is the quantity of blood required for transfusion, then the more dangerous is the undesirable phenomenon. This problem is substantially solved by the pumps of above type in which blood transference is performed without abrupt mechanical actions, i.e., peristaltically. The problem, however, has not been completely eliminated until now, and even while using the most advanced blood transfusion apparatus, medical personnel now and again register a patient's fever condition after transferring considerable quantities of blood, and additional efforts must be made to eliminate these after effects.
Specifically, in the description in U.S. Pat. No. 3,447,478 (Int.Cl.F 04 B 43/08), there is disclosed a "peristaltic" pump for blood transfusion, which includes features in which some of its roller members completely pinch the tube for transferring fluid, other roller members serving to adjust the amount of transferred fluid per unit of time by incomplete contraction of the tube aperture.
In the description of U.S. Pat. No. 4,012,177, there is disclosed a similar pump which has the same application and is provided with an improved construction of the tube allowing hemolysis during blood transference through the tube to be reduced.
None of the prior art pumps of the peristaltic type ensure complete elimination of hemolysis, and the pumps mentioned hereinabove are no exception. There still remains an urgent need to create a pump capable of transferring blood without substantial destruction of form elements ("hemolysis").
Additionally, the known pumps require relatively frequent replacement of the tube due to wear which means additional problems to the user.